1. Field of the Invention
The present invention relates to a method and an apparatus for diagnosing occurrence of misfire in an internal combustion engine.
2. Related art of the Invention
There has been conventionally proposed a misfire diagnosing apparatus for an internal combustion engine, in which the occurrence of misfire is judged based on periods of reference signals which are generated by a crank angle sensor at each crank angle 720.degree./n (n: number of cylinders) and are successively detected, and in response to fluctuation status of these periods (see Japanese Unexamined Utility Model Publication No.5-17172).
However, in such a case that the misfire diagnosis is performed in response to the fluctuation states of periods (angular speed) of the reference signals, there may have been erroneously detected such as particularly in a higher rotation and less load region in which the fluctuation of engine combustion rarely appears so that the misfire of a single cylinder and that of a plurality of cylinders cannot be distinguished from each other.